In the commercial production of crops such as corn, seeds are commonly exposed to suboptimal soil temperatures and excess water, which can reduce crop establishment and productivity. There are several factors contributing to the exposure of seeds to these unfavorable conditions. For example, farmers often favor early spring planting, when the likelihood of cold, wet conditions is higher, to enhance yields by extending the growing season and reduce the potential for drought during flowering. Also, farmers who manage large acreages commonly start planting early to ensure they complete planting in a timely manner.
The sensitivity of crop seeds, such as corn, to cold conditions during crop establishment is a major limitation to productivity and yield. For example, the proportion of corn seeds that emerge and produce normal plants is significantly reduced in fields where average soil temperatures are at or below 10° C. after planting (Saab and Butzen, 2004, Diagnosing Chilling and Flooding Injury to Corn Prior to Emergence. Crop Insights Vol. 14, No 4). Also, flooding conditions such as those present in excessively wet soils can significantly limit crop establishment after as little as one day (VanToai, 1993, Field Performance of Abscisic Acid-Induced Flood Tolerant Corn. Crop Science 33:344-346).
Predicting successful establishment for crop plants is important for helping farmers manage early-planting risks. Even though there are potential advantages to early planting, such as higher crop yields, various challenges and unknown factors exist for farmers who choose to plant early. For example, planting into cold soils may delay seedling emergence. Extreme cold or snow which occurs after planting may reduce germination rates and result in decreased crop establishment. Corn planted under irrigation may experience stress if the irrigation water is too cold. In addition, an increasing trend in planting practices is to use no-till or minimal tillage planting. This practice may increase the amount of water and organic matter in the soil and decreases erosion. No-till or minimal/reduced tillage planting may result in lower soil temperatures, more water retained in the crop residue, and slower seedbed drying. These conditions, depending on the particular year, can negatively impact seed germination and crop emergence. As such, the development of new crop varieties and the identification of existing crop varieties with improved seed tolerance to cold and flooding stress is needed. However, progress in this area has been limited by the availability of predictive methods for testing and selecting germplasm for stress tolerance.
Currently, the most accepted standard for assessing the ability of seeds to germinate under field conditions is the cold test (Association of Official Seed Analysts, 2002, Seed Vigor Testing Handbook, AOSA, Stillwater, Okla.). The general test procedure involves subjecting seeds to a non-flooding, 10° C. stress period followed by a grow-out period at 25° C. The cold test is widely conducted at public institutions such as Iowa State University and Michigan Crop Improvement Association (http://www.michcrop.com/seedtesting.asp), and at commercial companies such as Precision Seed Research (http://www.psrcorn.com/seedtesting.html#warmcoldgerm). However, the cold test, which was developed as early as the 1950's (Clark, 1953, Relationship Between Certain Laboratory Tests and the Field Emergence of Sweet Corn. Proc. Assoc. Off. Seed Anal. 1953:42-44) has been reported to be non-reliable for predicting field emergence under cold, wet conditions (Burriss and Navratil 1979, Relationship Between Laboratory Cold-Test Methods and Field Emergence in Maize Inbreds. Agronomy Journal 71: 985-988). Also, the temperature of the test is not predictive of soil temperatures experienced by seeds in early planted fields. Therefore, these tests are generally not predictive of stressful field conditions and do not show sufficient differentiation among hybrids or varieties to allow for germplasm selection.
In general, the moisture content of seeds has a large influence on their germination ability. In commercial seed corn production, for example, seeds are dried to approximately 12 to 13% moisture to maintain maximum germination potential (Wych, R. D. 1988. Production of Hybrid Seed Corn. pp. 565-607. In: Sprague, G. F., Dudley, J. W., Editors. Corn and Corn Improvement, Third Edition. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, Wis. 986 pp.). However, drying seed corn to lower moistures can significantly reduce germination ability under cold conditions as a result of injury to emerging seedling structures (Cohn, et al., (1979) Relationship of Stelar Lesions to Radicle Growth in Corn Seedling. Agronomy Journal 71:954-958). There are no known reports that demonstrate the use of drying to sub-optimal moisture content for genetic differentiation or selection for the ability to germinate and emerge under cold or flooding stress.
Herein, a soaking test was developed which closely reproduces cold, saturated field conditions commonly present in the field during early planting. This test can be used in combination with a method to dry the seed to sub-optimal moisture (ultra-drying) to identify hybrids or varieties with an improved ability to germinate and emerge under cold or flooding conditions.
Methods to impose stress on seeds in order to test germination and predict a seed's relative ability to emerge are disclosed herein. An advantage of this is the capability to evaluate the relative ability of genotypes to emerge under stressful field conditions.